Conventionally, organic coated substrates are cured in hot air ovens in which the substrate is exposed to temperatures of the range 150.degree.-210.degree. C. for a dwell time of about 10 minutes. This conventional curing technique involves the disadvantage that the carrier solvent of the coating is evaporated and produces harmful air pollution if released to the atmosphere.
In practice, most of the hot air containing the solvent vapors is normally recirculated for energy conservation considerations and as a result, the solvent vapors must be incinerated, at a significant cost in energy.
Water based coatings have been developed in an effort to reduce the air pollution resulting from curing. These coatings also include a small proportion of organic solvents and are limited for certain applications such as canning of foods.
Coatings which are curable by exposure to intense Ultra-Violet radiation are also known. These suffer from the disadvantages of high cost and relatively poor quality, which render them unsuitable for interior coating of cans containing foods.
The few systems which utilize heating for the coating of strips either force nitrogen gas to pass through the solvents, allowing this mixture to be incinerated or cooled by means of liquid nitrogen. These methods are employed because a high concentration of noncondensible gas in the vapor significantly reduces the efficiency of condensation.